Base-collector leakage currents in InP/InGaAs double heterojunctionbipolar transistors

For InP/InGaAs HBT's, base-collector leakage current can restrict their operation to a narrow emitter-collector voltage range. We studied several factors that can degrade the leakage current: the base-collector junction design, the base mesa etching technique, and the base metallization process. A step-graded base-collector heterojunction offered the best results. A leakage free multiple step etching process, combining wet and dry etching, has been developed. Ti/Pt/Au is a suitable base metallization, provided that the platinum layer is not too thick, and that the contact annealing temperature is not too high. Finally, very low leakage current HBT's were fabricated     

High-speed InP/InGaAs heterojunction bipolar transistors

Very-high-performance common-emitter InP/InGaAs single heterojunction bipolar transistors (HBTs) grown by metalorganic molecular beam epitaxy (MOMBE) are reported. They exhibit a maximum oscillation frequency (f_T) of 180 GHz at a current density of 1×10⁵ A/cm². this corresponds to an (R_BC_BC)_eff=f _T/(8πf²_max) delay time of 0.12 ps, which is the smallest value every reported for common-emitter InP/InGaAs HBTs. The devices have 11 μm² total emitter area and exhibit current gain values up to 100 at zero base-collector bias voltage. The breakdown voltage of these devices is high with measured BV_CEO and BV_CEO of 8 and 17 V, respectively     

Avalanche multiplication in InP/InGaAs double heterojunctionbipolar transistors with composite collectors

The experimental and theoretical studies of electron multiplication in InP/InGaAs double heterojunction bipolar transistors (DHBT's) with an InGaAs/InP composite collector are carried out. Both local electric field model and energy model are used to investigate the electron impact ionization in the composite collector. The analysis reveals that the nonlocal effect of the electron impact ionization in the composite collector is responsible for the suppression of the contribution of electron multiplication in the InGaAs layer. Experimental results for the fabricated devices were compared with the theoretical calculations, indicating that the conventional impact ionization models based on the local electric field significantly overestimate the electron multiplication for the composite collector. The energy model which takes into account the nonlocal effect is found to provide a more accurate prediction of electron multiplication for the DHBT's     

High-speed InGaAs(P)/InP double-heterostructure bipolar transistors

Double-heterostructure InGaAs(P)/InP bipolar transistors ranging in emitter size from 5 × 10 to 100 × 150 µm²have been fabricated using a non-self-aligned technology. These transistors exhibit current gains as high as 275 independent of emitter perimeter-to-area ratio. The best frequency of unity current gain was measured in the smallest devices to be 18 GHz. The high-frequency operation was mainly limited by the emitter charging time.     

Ultra-high-speed InP/InGaAs heterojunction bipolar transistors

We report on the microwave performance of InP/In_0.53Ga _0.47As heterojunction bipolar transistors (HBT's) utilizing a carbon-doped base grown by chemical beam epitaxy (CBE). The f_T and f_max of the HBT having two 1.5×10 μm² emitter fingers were 175 GHz and 70 GHz, respectively, at I_C=40 mA and V_CE=1.5 V. To our knowledge, the f _T of this device is the highest of any type of bipolar transistors yet reported. These results indicate the great potential of carbon-doped base InP/InGaAs HBT's for high-speed applications     

Subpicosecond InP/InGaAs heterostructure bipolar transistors

Bipolar transistors with subpicosecond extrinsic delay are discussed. These InP/InGaAs heterostructure transistors show a unity-current-gain cutoff frequency f_$T=165 GHz and maximum oscillation frequency f_MAX=100 GHz at room temperature. The authors model shows that an f_$T beyond 386 GHz is obtainable by further vertical scaling. Ring oscillators implemented with nonthreshold logic (NTL) and transistors having f_MAX=71 GHz show a propagation delay of 14.7 ps and 5.4 mW average power consumption per stage     

Selfaligned InGaAs/InP heterostructure bipolar transistors

InGaAs/InP heterostructure bipolar transistors have been realised using a new selfaligned process. Transistor wafers were grown by chemical beam epitaxy. Ideality factors close to unity were measured for emitter-base and collector-base diodes. The resulting devices exhibit nearly constant gain over four orders of magnitude of collector current densities, from j=1.5*10/sup -4/ A/cm/sup 2/ to 1.5 A/cm/sup 2/.<>     

High-speed InAlAs/InGaAs heterojunction bipolar transistors

InAlAs/InGaAs heterojunction bipolar transistors fabricated from wafers grown by molecular beam epitaxy are discussed. A cutoff frequency of 32 GHz for a collector current of 20 mA is achieved in the emitter area of devices 6×10 μm². The use of heavily doped and nondoped InGaAs layers as the emitter cap and collector, respectively, results in a reduction of the emitter and collector charging times; this, in turn, leads to improved microwave performance     

InGaAs/InP composite collector heterostructure bipolar transistors

A high speed bipolar transistor with high breakdown voltage BV/sub CEO/ is described. The structure uses a composite collector of InGaAs and InP. A common emitter gain of 65 is obtained with a base doping of 7*10/sup 19/ cm/sup -3/ and a breakdown voltage in excess of 10 V. The f/sub T/=64 GHz was reached at a collector-emitter voltage of 2 V and a current density of 52 kA/cm/sup 2/. The potential of this structure for very high speed applications is demonstrated by the extracted intrinsic transit time of 0.4 ps.<>     

InGaAs/InP heterobipolar transistors for integration on semi-insulating InP substrates

InGaAs/InP npn heterojunction bipolar transistors (HBTs) have been fabricated from LPE layers grown on semi-insulating InP substrates for application to integrated circuits. The inverted emitter configuration is used, which allows the growth of the active layers without any additional steps. The HBTs show stable characteristics without any hysteresis and with current gains up to 25 for 0.7 ?m base width. To our knowledge this is the first report of InGaAs/InP HBTs on a semi-insulating substrate.     

InP/InGaAs double-heterojunction bipolar transistors for high-speedoptical receivers

We fabricated monolithically integrated pin/HBT photoreceivers using FPIGA (full-potential InGaAs) DHBT's with various collector thicknesses. An HBT figure-of-merit was deduced from the relationship between measured bandwidths of the preamplifiers and the f_T's and f_max's of the DHBT's. A phenomenological device model of the DHBT's is proposed to find the optimum collector thickness that gives the highest bandwidth of the photoreceivers. Finally, we discuss the feasibility of monolithically integrating a pin-PD, preamplifier, buffer amplifier, and D-type flip-flop with an operating speed of 40 Gbit/s     

Be diffusion in InGaAs/InP heterojunction bipolar transistors

Classic signatures of Be diffusion were observed in InAlAs/InGaAs HBT's after elevated temperature bias stress, i.e., a positive shift in the Gummel plot, higher collector ideality, and higher offset voltage. An activation energy of 1.57 eV was calculated. Lifetimes of 3.3×106 h and 37000 h were extrapolated for low and high power operation, respectively. In contrast, an InP/InGaAs HBT with a C doped base showed no signatures of C diffusion. The results show that Be diffusion is manageable at lower power. They also support the idea that C is more stable than Be in this material system     

Co-integration of resonant tunneling and double heterojunctionbipolar transistors on InP

The authors report the first co-integration of resonant tunneling and heterojunction bipolar transistors. Both transistors are produced from a single epitaxial growth by metalorganic molecular beam epitaxy, on InP substrates. The fabrication process yields 9-μm²-emitter resonant tunneling bipolar transistors (RTBTs) operating at room temperature with peak-to-valley current ratios (PVRs) in the common-emitter transistor configuration, exceeding 70, at a resonant peak current density of 10 kA/cm², and a differential current gain at resonance of 19. The breakdown voltage of the In_0.53Ga_0.47As-InP base/collector junction, V_CBO, is 4.2 V, which is sufficient for logic function demonstrations. Co-integrated 9-μm²-emitter double heterojunction bipolar transistors (DHBTs) with low collector/emitter offset voltage, 200 mV, and DC current gain as high as 32 are also obtained. On-wafer S-parameter measurements of the current gain cutoff frequency (f_T) and the maximum frequency of oscillation (f_max) yielded f _T and f_max values of 11 and 21 GHz for the RTBT and 59 and 43 GHz for the HBT, respectively     

Breakdown-speed considerations in InP/InGaAs single- anddouble-heterostructure bipolar transistors

The breakdown and speed characteristics of InP/InGaAs single and double HBTs are presented. Temperature-dependent two- and three-terminal measurements suggest that avalanche impact ionization is the dominant breakdown mechanism in InGaAs collector HBTs. Monte Carlo techniques and 1D drift-diffusion modeling are used for speed and breakdown simulation, respectively. Special doping profiles are evaluated for improving the breakdown-speed characteristics of single HBTs (SHBTs) with conventional uniformly doped InGaAs collectors. Double HBTs (DHBTs) outperform all SHBTs in terms of speed-breakdown tradeoffs as long as they use graded base-collector junctions or they operate under sufficiently high collector-emitter voltage conditions. A cutoff frequency of 200 GHz was found to be feasible with graded DHBTs, and breakdown voltages up to 4.6 V were evaluated with a 3000-Å-thick collector. Nongraded DHBTs can be optimized to perform better in terms of speed-breakdown tradeoffs provided that a high collector doping is used     

On the storage time of InGaAs/InP bipolar transistors

The collector storage time was measured for InGaAs/InP bipolar transistors. For the evaluation, the transistors were driven into deep saturation choosing a test condition with no reverse base current. Devices comprising a homojunction- and a modified wide-gap-collector structure, respectively, were compared. For the latter device structure a marked reduction of the storage time by a factor of 10 was found.     

Magnetotransport characterization of surface-treated InP/InGaAs heterojunction bipolar transistors

The results of surface modification induced effects on InP/InGaAs single heterojunction bipolar transistors, as revealed by magnetotransport experiments, are described here. The surface treatments included both sulphur-based surface passivation and ion bombardment-induced surface damage. The former is known to improve device characteristics and the latter to degrade device operation. In this work the aim was to assess these techniques for tailoring device performance for surface sensing applications. Device characteristics were found to be sensitive to surface preparation prior to measurements. Measurements revealed that surface treatments that improve device performance also reduce sensitivity to external magnetic fields while treatments that degrade performance make devices more sensitive to externally applied magnetic fields.     

InP/InGaAs heterojunction bipolar transistors with different g-bridge structures

Several μ-bridge structures for InP-based heterojunction bipolar transistors (HBTs) are reported. The radio frequency measurement results of these InP HBTs are compared with each other. The comparison shows that μ-bridge structures reduce the parasites and double μ-bridge structures have a better effect. Due to the utilization of the double μ-bridges, both the cutoff frequency f_T and also the maximum oscillation frequency f_(max) of the 2×12.5 μm~2 InP/InGaAs HBT reach nearly 160 GHz. The results also show that the μ-bridge has a better effect in increasing the high frequency performance of a narrow emitter InP HBT.     

InP/InGaAs double heterostructure bipolar transistors grown by MBE

Double heterostructure bipolar transistors have been fabricated on InP/InGaAs MBE material. Current gains of up to 80 have been observed in the emitter-up configuration. The devices were fabricated using two diffusion techniques and selective etching to contact the base.     

High-speed InP/InGaAsP/InGaAs avalanche photodiodes grown bychemical beam epitaxy

High-performance InP/InGaAsP/InGaAs avalanche photodiodes (APDs) grown by chemical beam epitaxy are described. These APDs exhibit low dark current (less than 50 nA at 90% of breakdown), good external quantum efficiency (greater than 90% at a wavelength of 1.3 μm), and high avalanche gain (≃40). In the low-gain regime, bandwidths as high as 8 GHz have been achieved. At higher gains, a gain-bandwidth-limited response is observed; the gain-bandwidth product is 70 GHz     

Comparative investigation of InP/InGaAs abrupt, setback, and heterostructure-emitter heterojunction bipolar transistors

In this paper, the characteristics of InP/InGaAs abrupt, setback, and heterostructure-emitter heterojunction bipolar transistors (HBTs) are comparatively investigated by twodimensional simulation analysis. In the setback (heterostructure-emitter) HBT, a thin 50 ? undoped In_0.53Ga_0.47As (n-In_0.53Ga_0.47As) layer is inserted between n-InP emitter and p ⁺-InGaAs base layers to lower the energy band at emitter side for decreasing the collector-emitter offset voltage. The simulated results exhibits that the abrupt HBT has the largest current gain, the largest collector-emitter offset voltage, and the smallest unity gain cutoff frequency. While, the setback and heterostructure-emitter HBTs exhibit the smallest current gain and offcet voltage, respectively. Consequentially, the demonstration and comparison of the three-type HBTs provide a promise for design in circuit applications.